The present invention relates to a supply circuit for an eddy current probe. It is used in the non-destructive testing of metal parts, particularly tubes.
A known eddy current probe supply circuit is shown in FIG. 1. It comprises two channels 10.sub.1, 10.sub.2 operating in parallel. Each channel comprises an amplification circuit 12.sub.1, 12.sub.2, (which, in the illustrated example, is a differential amplifier), a reference winding 14.sub.1, 14.sub.2, and a resistor 16.sub.1, 16.sub.2 connected in negative feedback to the amplifierwinding means. Each channel has an input 18.sub.1, 18.sub.2 and an output 20.sub.1, 20.sub.2. The inputs are connected to a power supply 24, via an amplifier 26 of gain -1 for one of them (in the present case input 18.sub.1 of channel 10.sub.1). The output of each channel is connected to a coaxial cable 30.sub.1, 30.sub.2, supplying a probe formed by two windings 32.sub.1, 32.sub.2.
The outputs of amplifiers 12.sub.1, 12.sub.2 are connected by two resistors 34.sub.1, 34.sub.2. Their center makes it possible to extract a signal on connection D, said signal constituting a differential measurement of the unbalance of the probe. Two other resistors 36.sub.1, 36.sub.2 connect the output of one of the channels to the output of the amplifier of the other channel. Their center makes it possible to extract a signal on connection A, said signal constituting an absolute measurement.
This device has the disadvantage of lacking stability as a result of amplifiers 12.sub.1, 12.sub.2, which are simultaneously required to supply a high current to the probe and to control the voltage at the probe terminals (high pass band associated with a high output current).